Prioritized optical arbitration systems and methods

ABSTRACT

Various embodiments of the present invention relate to systems and methods for achieving low-latency, prioritized, distributed optical-base arbitration. In one embodiment, an optical arbitration system ( 100,1100 ) comprises a waveguide ( 102,1102 ) having a first end and a second end, and a source ( 104,1104 ) optically coupled to the first end of the waveguide and configured to input at least one wavelength of light into the waveguide. The system also includes a number of wavelength selective elements ( 106 - 109,1106 - 1109 ) optically coupled to the waveguide. Each wavelength selective element is capable of extracting a wavelength of light from the waveguide when activated by an electronically coupled node. An arbiter ( 110,116,120,1112,1116,1120 ) is optically coupled to the second end of the waveguide and to the waveguide between the source and a wavelength selective element located closest to the source along the waveguide.

TECHNICAL FIELD

Embodiments of the present invention relate generally to arbitration ofconcurrent requests for access to shared computer resources.

BACKGROUND

Modern distributed computer systems are typically composed of a numberof independently operating nodes. A node can be a processor, memory, acircuit board, a server, a storage server, a core or a multicoreprocessor, an external network connection or any other data processing,storing, or transmitting device. It is often the case that theseindependently operating nodes need access to the same resource. Forexample, two nodes may need to use an output port of another node fortransmitting information or need to use a shared resource such as ashared communication bus. Without coordination, these two nodes maybegin to simultaneously use the resource. It may be the case that theinformation sent by one or both of the nodes is lost or corrupted uponarrival at the resource. Thus, computer systems often employ a conflictresolution scheme called “arbitration” in order to prevent two or morenodes from simultaneously using the same resource. Arbitration ensuresthat only one node at a time uses the resource.

In many cases, arbitration lies on the critical path of computer systemperformance since arbitration inherently sequences two or more otherwiseindependent parallel activities. The nodes requesting access to aresource can be physically distributed. A typical arbitration schemeinvolves communication to gather all the “requests” for the resource, acentralized or distributed computation to select or “grant” one of therequests, and then an additional communication is needed to distributethe “grant” to the node which has won the arbitration.

The most critical property of any arbitration mechanism is the abilityto grant access to at most one requesting node at any given time. Thisarbitration property is typically called “mutual exclusion.” Fairness isanother property that is necessary to make an arbitration mechanismuseful in practice. In general, fairness implies that competing requestswill win arbitration with equal probability given a sufficiently largeenough sample of competing nodes. While this general interpretation offairness is often considered ideal, it is often expensive to achieve inpractice. This is particularly true for distributed arbitration schemeswhere the overhead incurred to achieve this general notion of fairnessoften results in reduced performance and increased cost. The overheadproblem becomes particularly impractical if cost and performance becomesignificantly worse as the system size increases. This “scaling” issueis particularly important for arbitration mechanisms which are intendedfor use in systems comprising a large number of nodes.

It is possible to relax this general notion of arbitration fairness to apolicy in order to provide “starvation free” arbitration. Whenarbitration is starvation free, it guarantees that any requesting nodewill eventually win the arbitration. While starvation free arbitrationusually incurs less overhead and has improved scaling properties whencompared to truly fair arbitration, it is problematic in that itinherently treats all requests at any given point in time as havingequal priority. In general, overall system performance is degradedsignificantly if certain requests are delayed to the point whereungranted requests become performance bottlenecks. In any system, somerequests have higher priority than others. Priority based arbitrationimplies that higher priority requests will be granted prior to lowerpriority requests. In priority based schemes, each new request isassigned an initial priority based on some importance metric. Anadditional option is to allow priorities to be increased based on howlong they have been waiting to win arbitration access to a particularresource. This “age based arbitration priority” can be coupled withstarvation free arbitration at each priority level to achieve anarbitration policy with reasonable fairness, scaling, and costproperties.

Any correct arbitration mechanism must be capable of guaranteeingmutually exclusive access to a shared resource, and must do so in a waythat is starvation free. Other desirable properties of an arbitrationmechanism include scalability in terms of cost and performance. The keyto cost scalability is minimizing the physical resources, such asenergy, wires, waveguides, and transistors, required to implement thearbitration policy, and the key to performance scalability is the needto reduce the latency of an individual arbitration decision as much aspossible. Engineers and computer scientists continue to develop lowerlatency arbitration systems and methods to increase system performance.

SUMMARY

Various embodiments of the present invention relate to systems andmethods for achieving low-latency, prioritized, distributed optical-basearbitration. In one embodiment, an optical arbitration system comprisesa waveguide having a first end and a second end, and a source opticallycoupled to the first end of the waveguide and configured to input atleast one wavelength of light into the waveguide. The system alsoincludes a number of wavelength selective elements optically coupled tothe waveguide. Each wavelength selective element is capable ofextracting a wavelength of light from the waveguide when activated by anelectronically coupled node. An arbiter is optically couple to thesecond end of the waveguide and to the waveguide between the source anda wavelength selective element located closest to the source along thewaveguide. Prioritized arbitration can be carried out by assigning eachwavelength a particular priority level or by assigning a priority levelto each time slot in which a portion of the at least one wavelength canbe extract from the waveguide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a first prioritized opticalarbitration system configured in accordance with embodiments of thepresent invention.

FIG. 2 shows tables representing the behavior of wavelength selectiveelements during an exemplary round of arbitration performed on anoptical arbitration system in accordance with embodiments of the presentinvention.

FIGS. 3A-3B show the arbitration system shown in FIG. 1 during a requestphase and a grant phase, respectively, of a round of arbitration inaccordance with embodiments of the present invention.

FIG. 4 shows a second exemplary timing diagram associated witharbitrating for two shared resources in accordance with embodiments ofthe present invention.

FIGS. 5A-5B show the arbitration system shown in FIG. 1 during a requestphase and grant phase, respectively, in accordance with embodiments ofthe present invention.

FIG. 6 shows a control-flow diagram representing steps associated with amethod for prioritized wavelength-division multiplexed arbitration for ashared resource in accordance with embodiments of the present invention.

FIG. 7A shows a circuit diagram of electronic components of a nodeconfigured in accordance with embodiments of the present invention.

FIG. 7B shows the node, shown in FIG. 7A, operated in accordance withembodiments of the present invention.

FIG. 8A shows a circuit diagram of electronic components of anelectronic circuit configured in accordance with embodiments of thepresent invention.

FIG. 8B shows the electronic circuit, shown in FIG. 8A, operated inaccordance with embodiments of the present invention.

FIG. 9 shows a schematic representation of a second optical arbitrationsystem configured in accordance with embodiments of the presentinvention.

FIG. 10 shows a schematic representation of a third optical arbitrationsystem configured in accordance with embodiments of the presentinvention.

FIG. 11 shows a schematic representation of a second optical arbitrationsystem configured in accordance with embodiments of the presentinvention.

FIG. 12 shows an example timing diagram associated with two rounds ofprioritized time-division multiplexed arbitration performed on theoptical arbitration system shown in FIG. 11 in accordance withembodiments of the present invention.

FIG. 13 shows a control-flow diagram representing steps associated witha method for prioritized time-division multiplexed arbitration for ashared resource in accordance with embodiments of the present invention.

FIG. 14 shows a circuit diagram of a node configured in accordance withembodiments of the present invention.

FIG. 15 shows a circuit diagram of a second electronic configured inaccordance with embodiments of the present invention.

FIG. 16A shows an isometric view of a microring resonator and a portionof an adjacent ridge waveguide disposed on the surface of a substrateand configured in accordance with embodiments of the present invention.

FIG. 16B shows a plot of transmittance versus wavelength for themicroring and waveguide shown in FIG. 16A.

FIG. 17 shows a microring resonator coupled to a detecting resonatorportion in accordance with embodiments of the present invention.

FIG. 18 shows a schematic representation and top view of doped regionssurrounding the microring and the ridge waveguide in accordance withembodiments of the present invention.

DETAILED DESCRIPTION

Various embodiments relate to systems and methods for achievinglow-latency, prioritized, distributed arbitration. The arbitrationsystems and methods are optical based, whereby different priority levelsfor accessing to a shared resource are associated with particularwavelengths of light or a single wavelength of light transmitted in aparticular time slot. The term “light” refers to electromagneticradiation having wavelengths within the visible and non-visible portionsof the electromagnetic spectrum, such as the ultraviolet and infraredportions of the spectrum. Separate wavelength prioritized arbitrationsystem and method embodiments are described below in a first subsectionand time-division multiplexed prioritized arbitration system and methodembodiments are described below in a second subsection.

I. Systems and Methods for Performing Prioritized Optical ArbitrationUsing Wavelength-Division Multiplexing A. An Optical Arbitration System

FIG. 1 shows a schematic representation of a first optical arbitrationsystem 100 configured in accordance with embodiments of the presentinvention. The system 100 includes a waveguide 102, an optical powersource 104 optically coupled to a first end of the waveguide 102, and 8substantially identical sets of four wavelength selective elementsrepresented by circles, such as circles 106-109. Each set of wavelengthselective elements is optically coupled to the waveguide 102 andelectronically coupled to one of 8 nodes labeled N0 through N7. Thesystem 100 also includes an arbiter comprising a detection element 110and a disable element 116. The detection elements 110 comprises fourdetecting wavelength selective elements 111-114 disposed near a secondend of the waveguide 102, and the disable element 116 comprises threedisabling wavelength selective elements 117-119 optically coupled to thewaveguide 102 between the source 104 and node N0. The arbiter alsoincludes an electronic circuit 120 that is electronically coupled to thedetecting wavelength selective elements 111-114 and the disablingwavelength selective elements 117-119.

As shown in the example of FIG. 1, light comprising fourdistinguishable, unmodulated wavelengths, each wavelength represented bya differently patterned directional arrow, is output from the opticalpower source 104 and injected into the waveguide 102. The light travelsin a counter-clockwise manner along the waveguide 102, as indicated bydirectional arrows 122-124, passing the disable element 116, each set ofwavelength selective element, and finally the detection element 110.Each wavelength represents a particular priority level associated withthe use of a resource, such as a bus waveguide, a port, or any othershared resource that only one node can use at a time. FIG. 1 andsubsequent figures include a legend 126 displaying four line patterns.Each line pattern represents a wavelength of light output from thesource 104 and each wavelength is associated with a particular prioritylevel. Dotted line pattern 127 represents a wavelength of light havingthe highest priority level 1, dot-dashed line pattern 128 represents awavelength of light having the second highest priority level 2, dashedline pattern 129 represents a wavelength having the third highestpriority level 3, and double-dot dashed line pattern 130 represents awavelength having the lowest priority level 4.

The waveguide 102 can be a ridge waveguide, a photonic crystalwaveguide, or an optical fiber. Examples of wavelength selectiveelements are microring resonators, photonic crystal resonators, or anyother device configured to have resonance with light of a particularwavelength traveling in the adjacent waveguide 102. The resonators aredisposed adjacent to the waveguide 102. This resonance enables aresonator to extract light of a particular wavelength from the waveguide102 via evanescent coupling. In the interest of brevity, the node,disabling, and detecting resonators are hereinafter referred to as “noderesonators,” “disabling resonators,” and “detecting resonators,”respectively. A more detailed description of the operation of mirroringresonators is provided below in the subsection “Mirroring Resonators.”

The node resonators and the disabling resonators are electronicallytunable, and each node resonator and each disabling resonator isconfigured to have resonance with one of the 4 wavelengths output fromthe source 104 when an appropriate voltage is applied, in which case thenode resonator or disabling resonator is said to be “active.” As shownin FIG. 1, each node and disabling resonator is illustrated with aparticular line pattern in order to identify the wavelength that eachresonator has resonance with when active. For example, node resonator106 has resonance with the wavelength 127 when active, and noderesonator 107 has resonance with the wavelength 128 when active. When atunable resonator is active, it extracts and traps light of anassociated wavelength from the waveguide 102 via evanescent coupling. Incertain embodiments, the node resonators, unlike disabling resonators,can be configured to convert at least a portion of the trapped lightinto an electronic signal that is transmitted to an electronicallycoupled node which interprets the electronic signal to indicate that thewavelength is removed from the waveguide 102. In other embodiments, thelight extracted by an activated node resonator is coupled into aseparate waveguide that carries the light to a detector. In general, thelight trapped in a resonator ultimately decays and leaks out via losses.While a resonator is active, the intensity or amplitude of the resonantwavelength carried by the waveguide 102 drops sharply to approximatelyzero. When the voltage is no longer applied, the resonance wavelength ofthe resonator shifts away from the wavelength of the light, theintensity or amplitude of the wavelength is restored, and the wavelengthpropagates undisturbed along the waveguide 102. When no voltage isapplied to a tunable resonator, the resonator is said to be “inactive.”

Unlike the node resonators and disabling resonators, the detectingresonators 111-114 of the detection element 110 are configured to be ina permanently active or resonant state. In other words, the detectingresonators 111-114 are not electronically tunable, and each detectingresonator is configured to have at least partial resonance with one ofthe wavelengths 127-130. As shown in FIG. 1, each detecting resonator inthe detection element 106 is also represented by a line patterncorresponding to one of the wavelengths 127-130 in order to identify thewavelength each detecting resonator has at least partial resonance with.Thus, each detecting resonator extracts at least a portion of the lightof a corresponding wavelength from the waveguide 102 via evanescentcoupling. When light is trapped within a detecting resonator, thedetecting resonator generates a relatively high electronic signal thatis transmitted along an electronically connected signal line to theelectronic circuit 120. When light is not trapped within a detectingresonator, the detecting resonator can transmit either a relatively lowelectronic signal to the electronic circuit 120 or transmit noelectronic signal to the electronic circuit 120. The electronic circuit120 receives the electronic signals from the detecting resonators111-114 and determines which priority levels should be disabled andactivates the appropriate disabling resonators 117-119 as describedbelow.

B. Wavelength-Division Multiplexed Arbitration

Arbitration is carried out on the system 100 in successive rounds. Eachround of arbitration includes (1) a request phase followed by (2) agrant phase. During the request phase the disabling resonators areinactive allowing the nodes participating in the round of arbitration toextract a wavelength associated with the priority level selected by theparticipating nodes. The detecting resonators 111-114 communicate to theelectronic circuit 120 which priority levels have been selected by thenodes during the request phase. At the beginning of the grant phase, theelectronic circuit 120 responds to the signals sent from the detectingresonators 111-114 by activating appropriate disabling resonators of thedisable element 116 to remove the wavelengths associated with prioritylevels that are lower than the highest priority level selected by one ofthe nodes. As a result, the node located closest to the source 104 thatsuccessfully extracted the wavelength associated with the highestpriority level during the request phase is granted access to theresource during the successive grant phase. During the grant phase, arequesting node that detects the wavelength associated with the prioritylevel of its request is aware that it has won the round of arbitrationand can be begin using the resource for a period of time. Also duringthe grant phase, the nodes not detecting the wavelength associated withthe priority level they selected during the request phase are aware thatthey have lost the round of arbitration and must wait for a subsequentround of arbitration.

FIG. 2 shows Tables A and B representing the behavior of the resonatorsduring an exemplary round of arbitration performed on the opticalarbitration system 100 in accordance with embodiments of the presentinvention. In particular, Table A represents the behavior of thedetecting resonators 111-114 and disabling resonators 117-119 of thesystem 100 during a round of arbitration, and Table B represents thebehavior of the node resonators of the system 100 during the same roundof arbitration. The entries corresponding to the priority levels 1-4 arerepresented by PLn, where n equals 1, 2, 3, or 4. In the followingdescription reference is made to FIGS. 3A-3B which show the arbitrationsystem 100 during a request phase and a grant phase, respectively, forthe round of arbitration represented in Tables A and B in accordancewith embodiments of the present invention.

In Table A, columns 201 and 202 display the priority levels orwavelengths removed from the waveguide 102 during the request and grantphases. At the beginning of the round of arbitration, the entries incolumn 201 are empty indicating that the disabling resonators 117-119are inactive and the wavelengths associated with the priority levels 1-4enter the waveguide 102. Each node asserting a request activates theresonator corresponding to the wavelength associated with the prioritylevel selected by the nodes. In Table B, column 203 represents thepriority levels selected by the nodes at the beginning of the round ofarbitration, and column 204 represents the wavelengths associated withthe priority levels each node attempts to extract during the requestphase. For example, column 203 reveals that node N1 selected prioritylevel 4, and column 204 reveals that node N1 activated the noderesonator corresponding to the wavelength associated with priority level4. Resonators remain active for the entire round of arbitration.

As shown in FIG. 3A, active resonators are shaded and an inactiveresonator is unshaded. Active resonators 301-306 correspond to thepriority levels represented in column 204 of Table B shown in FIG. 2. Asshown in the example of FIG. 3A, the four active resonators 301-303 and305 extract the wavelengths corresponding to the priority levels 1-4from the waveguide 102 as the wavelengths pass nodes N1-N3 and N6. NodesN5 and N7 activated resonators corresponding to the same priority levelsas nodes N4 and N1, respectively, however, because nodes N1 and N4 arelocated closer to the source 104 along the waveguide 102, nodes N1 andN4 extract the wavelengths before nodes N5 and N7.

Returning to FIG. 2, column 205 of Table B displays which nodessuccessfully extract and detect the wavelengths during the requestphase, where a detector value “0” represents no detection and a detectorvalue “1” represents detection. For example, in column 205 entries witha “1” reveal that nodes N1-N3 and N6 detected the wavelengths associatedwith priority levels selected by nodes N1-N3 and N6 and entries with a“0” reveal that nodes N5 and N7 did not detect the wavelengthsassociated with the priority levels they selected, as described abovewith reference to FIG. 3A. Because the wavelengths are completelyextracted by the nodes N1-N3 and N6, column 206 of Table A reveals thatat the end of the request phase, the detecting resonators 111-114 detectno light for each of the priority levels. For example, as shown in FIG.3A, the wavelengths associated with priority levels 1-4 are extracted byactive resonators 301-303 and 305 and none of the wavelengths reach thedetecting resonators 111-114.

Because the wavelengths associated with the highest priority level wasnot detected at the end of the request phase by the detecting resonator111, at the beginning of the grant phase, the electronic circuit 120activates the disabling resonators 117-119 so that wavelengths otherthan the highest priority level are extracted from the waveguide 102. Asshown in FIG. 3B, at the beginning of the grant phase, the electroniccircuit 120 activates all three of the disabling resonators 117-119. Asa result, the wavelengths corresponding to the priority levels 2-4 areextracted from the waveguide 102 leaving the wavelength corresponding tothe highest priority level to travel along the waveguide 102 where it isextracted by node N6.

Returning to FIG. 2, column 207 of Table B reveals that resonators301-306 remain active during the grant phase. The entries associatedwith the priority levels 2-4 in column 202 of Table A correspond to thewaveguides extracted by the disabling resonators 117-119 during thegrant phase, and column 208 has an entry of “1” for node N6, whichcorresponds to node N6 extracting the wavelength associated with thehighest priority level and winning the round of arbitration, asdescribed above with reference to FIG. 3B. The entries in column 209 areall “0” indicating that none of the wavelengths reach the detectingresonators 111-114 during the grant phase.

C. Combined Wavelength-Division Multiplexed and Time-DivisionMultiplexed Arbitration

In many computational systems, the nodes may share more than oneresource. For example, a number of nodes may need to access a buswaveguide and a number of nodes may also at about the same time need toaccess a shared output port. Thus, WDM-based arbitration methods can beexpanded to include time-division multiplexed (“TDM”) so thatarbitration can be carried out for multiple resources with the samearbitration system 100. The is accomplished by time-divisionmultiplexing separate request and grant phases within each round ofarbitration, where each pair of request and grant phases are associatedwith determining access to a different shared resource.

FIG. 4 shows a second exemplary timing diagram associated witharbitrating for two shared resources using the system 100 in accordancewith embodiments of the present invention. A single round of arbitrationincludes a first request phase 401 immediately followed by a first grantphase 402 and a second request phase 403 immediately followed by asecond grant phase 404. The first request phase 401 begins at time step0, and the second request phase 403 begins at time step 4. A time stepcan be a clock edge of a clock signal or any other suitable delineationfor discrete periods of time. Each request phase and grant phase spanseight time slots, where a time slot can be a single clock cycle, afraction of a clock cycle, a number of clock cycles, or any othersuitable period of time. Each time slot begins and ends on a time steprepresented by regularly spaced lines identified by an integers 0-35.Column 406 lists the priority request made by the nodes for the firstresource, and column 408 lists the priority requests made by the samenodes for the second resource. Each node has a particular time slotwithin a request phase in which it can assert a request, and each nodehas a particular time slot within a grant phase in which it learns thatits request is granted or denied. For example, node N0 is allowed toassert a request during the first request phase 401 for one time slotbeginning at time step 0, and node N1 is allowed to assert a request forthe same resource during the first request phase 401 for one time slotbeginning at time step 1. In addition, node N0 is allowed to assert arequest during the second request phase 403 for one time slot beginningat time step 4, node N1 is allowed to assert a request for the sameresource during the first request phase 401 for one time slot beginningat time step 5. Table I displays nodes and corresponding time steps whena node can activate a resonator for one time slot to assert a requestfor two resources during the request phases 401 and 403.

TABLE I Time step in Time step in Node request phase 1 request phase 2N0 0 4 N1 1 5 N2 2 6 N3 3 7 N4 4 8 N5 5 9 N6 6 10 N7 7 11

Each node that successfully asserts a request in one of the requestphases 401 and 403 can determine whether or not that request has beengranted during the corresponding first and second grant phases 402 and404 by activating the resonator corresponding to the selected prioritylevel for one time slot during the grant phases 402 and 404. Table IIdisplays nodes and corresponding time steps when each node can activatea resonator in the respective grant phases 402 and 404.

TABLE II Time step in Time step in grant Node grant phase 1 phase 2 N0 812 N1 9 13 N2 10 14 N3 11 15 N4 12 16 N5 13 17 N6 14 18 N7 15 19

As shown in the example of FIG. 4, column 406 reveals that nodes N2, N3,and N6 have all selected the second priority level. Node N2 beginsextracting the wavelength 128 at time step 2 leaving a one time slot gap412 in the wavelength 128 travelling around the waveguide 102, and nodeN5 begins extracting the wavelength 129 at time step 5 leaving a onetime slot gap 414 of in the wavelength 129. The gaps associated with thefirst request phase 401 are labeled 1. FIG. 4 reveals that gap 412reaches nodes N3 at the beginning of time steps 3 and reaches node N6 atthe beginning of time steps 6, which corresponds to the time steps whennodes N3 and N6 are allowed to assert a request for the priority levelassociated with the wavelength 128. Thus, nodes N3 and N6 fail toextract the wavelength 128 beginning at time steps 3 and 6, and as aresult, nodes N3 and N6 have to wait for a later round of arbitration toassert another request for the first resource.

FIGS. 5A-5B show the arbitration system 100 during the request phase 401and the grant phase 402, respectively, operated in accordance withembodiments of the present invention. Active resonators 501-504correspond to the circled nodes in column 406 in FIG. 4. Integerslocated next to each node correlate with the time steps in the requestand grant phases 401 and 402. As shown in the example of FIG. 5A, activeresonator 501 extracts a corresponding wavelength from the waveguide 102when activated at time step 2, which corresponds to the gap 412 in FIG.4, and active resonator 503 extracts a corresponding wavelength from thewaveguide 102 when activated at time step 5, which corresponds to thegap 418 in FIG. 4. The wavelengths 127 and 130 pass the sets ofresonators undisturbed and are detected by the detecting resonators 111and 114 during the time slot beginning at time step 7. The detectingresonator 111 sends an electronic signal to the electronic circuit 120.As shown in FIG. 5B, the electronic circuit 120 responds by activatingthe disabling resonators 118 and 119 for a period of one time slot. Atthe beginning of the grant phase 402, which begins at time slot 8 asshown in FIG. 4, the wavelengths 129 and 130 are extracted from thewaveguide 102 leaving the wavelengths 127 and 128 to continue travelingalong the waveguide 102 where the wavelength 128 is extracted by node N2at time step 10.

Returning to FIG. 4, beginning with the first grant phase 402 at timeslot 8, the wavelengths 129 and 130 are extracted from the waveguide 102for one time slot leaving gaps 420 and 422 in wavelengths 129 and 130,as described above with reference to FIG. 5B. At the beginning of thetime step 10, the node N2 extracts the wavelength 128 for one time slotleaving a one time slot gap 416 in the wavelength 128. Thus, node N2 isaware that it has been granted access to the first resource until thestart of the first grant phase of the next round of arbitration and canbe begin using the resource.

Meanwhile, column 408 reveals that node N0 selected the lowest prioritylevel and node N3 selected the highest priority level. The gapsassociated with the request 403 and grant phase 404 are labeled 2. Thetiming diagram reveals that node N3 is ultimately granted access to thesecond resource at time step 15.

D. Increasing Priority Levels

The arbitration methods described above with reference to FIGS. 2-5favor nodes that lie closest to the optical power source 104. Forexample, suppose nodes N3 and N6 both select the same priority level atthe beginning of the request phase. Provided no other node has selecteda higher priority level, node N3 will be granted access and node N6 hasto wait for a subsequent round of arbitration to assert another request.Embodiments of the present invention also allow nodes to increment orincrease the priority level when they have either lost request or won arequest but lost access during the grant phase. Increasing the prioritylevel can be based on a class of service agreement, type of informationto be transmitted, global age of information, length of time informationhas been stored at the node, present length of time before informationexpires, or any other criteria for determining an increase in thepriority level. For example, suppose node N6 processes packets that aretime stamped and must be sent before the packets expire. In certainembodiments, after each unsuccessful round of arbitration, node N6 canre-examine the time stamp on each packet and accordingly increase thepriority level. In other embodiments, node N6 can increase the prioritylevel immediately following an unsuccessful request phase or immediatelyfollowing an unsuccessful grant phase.

E. Summary of Wavelength-Division Multiplexed Arbitration

FIG. 6 shows a control-flow diagram representing steps associated with amethod for performing prioritized WDM arbitration for a shared resourcein accordance with embodiments of the present invention. As shown inFIG. 6, steps 602-607 are steps performed during a request phase, andsteps 608-613 are performed during a grant phase. In step 601, lightcomprising a number of wavelengths is injected from an optical powersource into a waveguide using wavelength-division multiplexing, asdescribed above with reference to FIG. 1. Each wavelength of light isassociated with a particular priority level. In step 602, the methodenters the request phase, and nodes electing to participate in a roundof arbitration each select a priority level for accessing to a sharedresource. The nodes electing to participate have no knowledge of thepriority levels selected by other participating nodes, and thus, eachnode independently selects a priority level. In step 603, the nodeselecting to participate, activate a resonator corresponding to thewavelength of light associated with the selected priority level, asdescribed above with reference to FIGS. 1, 3A, and 5A. In step 604, eachnode that extracts a selected wavelength of light proceeds to step 605,otherwise, each node that does not extract a wavelength of lightproceeds to step 606. In step 606, nodes are aware that they lost theirrequest, deactivate their resonators, and wait for a later round ofarbitration to assert a new request for access to the resource. Inoptional step 607, a node that is unsuccessful in asserting a requestcan increment the priority level in order to increase the node's chancesof success in a subsequent round of arbitration. For example, a nodesending VoIP packets may increase to the highest priority level for asubsequent round of arbitration or a node can increment the prioritylevel associated with certain packets that are time stamped and have tobe sent before they expire. In step 605, the remaining participatingnodes are aware that they won their request and proceed to the grantphase to determine whether their request is granted or denied. Inoptional step 608, the nodes that won their request to proceed to thegrant phase can leave their resonators active, as described above withreference to FIGS. 4-5, or they can deactivate their resonators andreactivate their resonators during the grant phase, as described abovewith reference to FIGS. 2-3. In step 609, wavelengths associated withpriority levels that are lower than the highest extracted priority levelwavelength are removed from the waveguide, as described above withreference to FIGS. 3B and 5B. In step 610, when the node having selectedthe highest priority level that is located closest to the optical powersource extracts the associated wavelength from the waveguide proceed tostep 611, otherwise, the remaining nodes proceed to step 612. In step611, the node is granted access to the resource, and in subsequent step613, the node begins using the resource. In step 612, the remainingnodes are aware that they are not granted access to the resource andwait for a subsequent round of arbitration. In optional step 614, thesenodes can increment their selected priority levels for subsequent roundsof arbitration. In step 615, the steps 601-613 are repeated forsubsequent rounds of arbitration.

F. Schematic Circuit Diagrams of Nodes, the Electronic Circuit, andOther Optical Arbitration System Embodiments

FIG. 7A shows a schematic circuit diagram of a node 700 configured inaccordance with embodiments of the present invention. The node 700represents the nodes of the optical arbitration system 100. Theelectronic components include an enablement circuit (“ENB”) 702, an ORgate 704, and a request latch 706. The request latch 706 iselectronically coupled to the ENB 702 which is electronically coupled toeach of the resonators 708-711. The resonators 708-711 are eachseparately electronically coupled to the OR gate 704. Each resonator isassigned a 2-bit priority level corresponding to one of the fourpriority levels assigned to the wavelengths 127-130. In particular, the2-bit priority levels assigned to the resonators 708-711 can be “00,”“01,” “10,” and “11,” respectively, which are listed below eachresonator in FIG. 7A, and where “00” corresponds to the highest prioritylevel, “01” corresponds to the second highest priority level, “10”corresponds to the third highest priority level, and “11” corresponds tothe lowest priority level. The bits “0” and “1” can be realized byassigning the bit “0” to a low or no electronic signal and the bit “1”to a relatively high electronic signal. The resonators 708-711 areconfigured to extract the corresponding wavelengths 127-130 from thewaveguide 102 when activated. The request latch 706 receives electronicsignals from the node at inputs D1, D2, D3 and the system clock signalat CLK. The two inputs D1 and D2 receive the 2-bit priority level andthe third input D3 receives an electronic request signal indicating thatthe node is ready to activate the resonator associated with the 2-bitpriority level. The request latch 706 outputs the 2-bit priority leveland the request signal on either the rising or falling edge of the clocksignal. The ENB 702 receives the 2-bit priority level and the requestsignal and activates the resonator associated with the 2-bit prioritylevel.

FIG. 7B shows an exemplary operation of the node 700 in accordance withembodiments of the present invention. Assume that the node 700 in anindependent operation selects the second highest priority level inrequesting access to a shared resource. The node 700 then sends the2-bit priority level “01” to the request latch 706 which stores the bitsuntil the request latch 706 receives a request signal. When the node 700is ready to request access to the resource, the node 700 sends a requestsignal to the request latch 706 which simultaneously and separatelylatches the bits “0” and “1” into the inputs S1 and S2 and latches therequest signal to the ENB 702 on either a rising or falling time step ofthe clock signal. The ENB 702 upon receiving the 2-bit priority levelactivates the corresponding resonator 709. The activated resonator 709is shaded, and the inactive resonators 708, 710, and 711 are unshaded.As shown in FIG. 7B, the activated resonator 709 extracts thecorresponding wavelength 128 from the waveguide 102. The otherwavelengths 127, 129, and 130 pass the resonators 708, 710, and 711undisturbed. The activated resonator 709 sends an electronic signal tothe OR gate 704, which responds by sending a signal to node 200. Thenode interprets the signal to mean that the node has successfullycompleted a request for access to the resource. The operation isrepeated during the grant phase.

FIG. 8A shows a circuit diagram of the electronic circuit 120 configuredin accordance with embodiments of the present invention. The componentsof the electronic circuit 120 include an inverter 802, a first NAND gate804, and a second NAND gate 806. FIG. 8A reveals how the detectingresonators 111-113 are electronically coupled to the inverter 802 andNAND gates 804 and 806. The detecting resonator 114 extracts the lowestpriority wavelength 130 from the waveguide 102 in order to keep thewavelength 130 from being reflected back into the waveguide 102.

When the wavelength 127 is detected by the detecting resonator 111,electronic signals are input from the detecting resonator 111 to theinverter 802 and NAND gates 804 and 806. When the wavelength 128 isdetected by the detecting resonator 112, electronic signals are inputfrom the detecting resonator 112 to the NAND gates 804 and 806. When thewavelength 129 is detected by the detecting resonator 113, electronicsignals are input from the detecting resonator 113 to the NAND gate 806.The inverter 802 outputs electronic signals to the disabling resonator117, and the NAND gates 804 and 806 output electronic signals to thedisabling resonators 118 and 119, respectively. As described above, eachof the detecting resonators 111-113 generates relatively high electronicsignals when light of a corresponding wavelength is trapped in thedetecting resonator and generates a relative low or no electronic signalwhen no light is trapped in the detecting resonator. The inverter 802converts a relatively high electronic signal received from the detectingresonator 111 into a relatively low electronic signal that is sent tothe disabling resonator 117 and converts a relatively low or noelectronic signal received from the detecting resonator 117 into arelatively high electronic signal that is sent to the disablingresonator 117. The NAND gates 804 and 806 output a low or no electronicsignal to the disabling resonators 118 and 119 when all of the inputelectronic signals are relatively high and output a relatively highelectronic signal to the disabling resonators 118 and 119 when at leastone of the input electronic signals is low.

FIG. 8B shows the electronic circuit, shown in FIG. 8A, operated inaccordance with embodiments of the present invention. Detectingresonators 112 and 114 extract the wavelengths 128 and 130,respectively, and the wavelengths 127 and 129 do not reach the detectingresonators 111 and 113. The wavelengths 127 and 129 may have beenextracted by nodes along the waveguide, as described above withreference to FIG. 2. In other words, a node has selected the highestpriority level and another node has selected the third highest prioritylevel during the request phase. As a result, the detecting resonator 112sends relatively high electronic signals to the NAND gates 804 and 806.On the other hand, the detecting resonator 111 sends a low or noelectronic signal to the inverter 802 and to an input of the NAND gate804, and the detecting resonator 113 sends a low or no electronic signalto an input of the NAND gate 806, respectively. The inverter 802responds to the low or no electronic signal received from the detectingresonator 111 by sending a high electronic signal that activates thedisabling resonator 117. The NAND gate 804 responds to low and relativehigh electronic signals received from the detecting resonators 111 and113, respectively, by activating the disabling resonator 118. Finally,the NAND gate 804 responds to low electronic signals sent by thedetecting resonators 111 and 113 and the relative high electronicsignals received from the detecting resonator 112 by activating thedisabling resonator 119. The active disabling resonators 117-119 areshaded and extract the wavelengths 128-130 from the waveguide 102leaving the highest priority wavelength 127 to propagate along on thewaveguide 102 so that the node having selected the highest prioritylevel can extract the wavelength 127 and realize that it has beengranted access to the resource. Meanwhile the node that extracted thethird highest priority level does not extract the wavelength 129 duringthe grant phase and realizes that it has not been granted access to theresource.

Arbitration system embodiments are not limited to eight nodes and theparticular arrangement of nodes shown in FIG. 1. Arbitration systemembodiments can be configured to provide prioritized optical arbitrationfor any number of nodes having any possible arrangement. FIG. 9 shows aschematic representation of a second optical arbitration system 900configured in accordance with embodiments of the present invention. Thesystem 900 includes a waveguide 902, the optical power source 104optically coupled to a first end of the waveguide 902, and 8 sets offour resonators. The system also includes the disable element 116disposed between the source 104 and node N0, the detection element 110optically coupled to a second end of the waveguide 902, and theelectronic circuit 120 electronically coupled to the disablingresonators 117-119 of the disable element 116 and the detectingresonators 111-114 of the detection element 110. The resonators and thewaveguide 902 are configured so that the a first portion of thewaveguide 904 is adjacent to all of the resonators associated with thehighest priority level, a second portion of the waveguide 906 isadjacent to all of the resonators associated with the second highestpriority level, a third portion of the waveguide 908 is adjacent to allof the resonators associated with the third highest priority level, anda fourth portion of the waveguide 910 is adjacent to all of theresonators associated with the lowest priority level.

Arbitration system embodiments are not limited to a single waveguideconfigured to carry the wavelengths associated with each priority level,such as waveguides 102 and 902. In other embodiments, each wavelengthcan be transmitted in a separate waveguide. FIG. 10 shows a schematicrepresentation of a third optical arbitration system 1000 configured inaccordance with embodiments of the present invention. The system 1000includes four separate waveguides 1002-1005, an optical power source 104optically coupled to a first end of each of the waveguides 1002-1005,and 8 sets of four resonators. The system 400 also includes the disableelement 116 disposed between the source 104 and node N0, the detectionelement 110 optically coupled to the second ends of the waveguides1002-1005, and the electronic circuit 120 electronically coupled to thedisabling resonators 117-119 of the disable element 116 and thedetecting resonators 111-114 of the detection element 110. Thewaveguides 1002-1005 separately carry the four wavelengths 127-130,respectively. The resonators associated with highest priority level aredisposed adjacent to the waveguide 1002, the resonators associated withsecond highest priority level are disposed adjacent to the waveguide1003, the resonators associated with third highest priority level aredisposed adjacent to the waveguide 1004, and the resonators associatedwith lowest priority level are disposed adjacent to the waveguide 1005.

II. Systems and Methods for Performing Prioritized Optical ArbitrationUsing Time-Division Multiplexed Arbitration A. An Optical ArbitrationSystem

FIG. 11 shows a schematic representation of an optical arbitrationsystem 1100 configured in accordance with embodiments of the presentinvention. The system 1100 includes a waveguide 1102, an optical powersource 1104 optically coupled to a first end of the waveguide 1102, andfour substantially identical node resonators 1106-1109. Each noderesonator is optically coupled to the waveguide 1102 and electronicallycoupled to one of four nodes labeled N0 through N3. The system 1100 alsoincludes an arbiter comprising a detection element 1112 and a disableelement 1116. The detection element 1112 comprising a detectingresonator 1114 disposed near a second end of the waveguide 1102, and thedisable element 1116 comprising a disabling resonator 1118 opticallycoupled to the waveguide 1102 between the source 1104 and node N0. Thearbiter also includes an electronic circuit 120 that is electronicallycoupled to the detecting resonator 1114 and the disabling resonator1118. As shown in the example of FIG. 11, light comprising a singleunmodulated wavelength is output from the optical power source 1104 andinjected into the waveguide 1102. The light travels in acounter-clockwise manner along the waveguide 1102, as indicated bydirectional arrows 1122-1124, passing the disable element 1116, eachnode resonator, and finally arrives at the detection element 1112. Thewaveguide 1102 can be a ridge waveguide, a photonic crystal waveguide,or an optical fiber. The resonators 1106-1109, detecting resonator 1114,and disabling resonator 1118 can be configured and operated as describedabove with reference to FIG. 1.

B. Time-Division Multiplexed Arbitration

Prioritized arbitration can be carried out on the arbitration system1100 by time-division multiplexing the priority levels within each roundof arbitration. Consistent with the prioritized WDM arbitrationdescribed above, each round of prioritized TDM arbitration is carriedout with (1) a request phase followed by (2) a grant phase. At thebeginning of the request and grant phases a token is injected into thewaveguide 1102. The token is a pulse of light having a particularwavelength and finite duration. Each portion of the token is associatedwith a particular priority level. For example, a token associated withthree prior levels comprises three portions with the first portionpassing a node associated with the highest priority level, the secondportion passing the node associated with the second highest prioritylevel, and the third portion passing the node associated with the lowestpriority level. The time when the token passes each node is differentdue to the distance between nodes, which is a fixed offset. In order fora node to assert a request or determine whether or not a request isgranted for a particular priority level, the node extracts the portionof the token corresponding to the priority level. For example, a firstnode asserting a priority level 2 request in a system employing threepriority levels extracts the middle portion of the token leaving a gapbetween the first and third portions of the token. A second node locatedfarther along the waveguide 1102 and asserting a priority level 1request extracts the first portion of the token. Thus, unlike wavelengthdivision multiplexing were each priority level is associated with aparticular wavelength of light, in time-division multiplexing, eachpriority level is associated with a particular portion of the token.

FIG. 12 shows an example timing diagram associated with two rounds ofprioritized TDM arbitration performed on the system 1100 in accordancewith embodiments of the present invention. The first round ofarbitration includes a first request phase 1201 followed by a firstgrant phase 1202, and the second round of arbitration includes a secondrequest phase 1203 followed by a second grant phase 1204. Column 1205lists the node labels N0 through N3 and a label D representing thedetection element 1114 in FIG. 11. A table 1206 displays the node labelsN0 through N3 and lists in columns the priority levels selected by thenodes for two rounds of arbitration. The nodes have three prioritylevels to select from. For example, in the first round of arbitration,nodes N0, N1, and N3 selected priority levels 2, 1, and 3, respectively,and node N2 has elected not to participate. The time slots are labeledwith the priority levels in which each node can assert a request orlearn that a successful request has been granted or denied. For example,node N0 can assert a priority level 1 request 1207 beginning at timestep 0, assert a priority level 2 request 1208 beginning at time step 1,and assert a priority level 3 request 1209 beginning at time step 2. Inaddition, node N0 can learn whether or not a priority level 1 requesthas been granted 1210 beginning with time step 5, learn whether or not arequest for a priority level 2 request has been granted 1211 beginningwith time step 6, and learn whether or not a request for a prioritylevel 3 has been granted 1212 beginning with time step 7. A node wins arequest or is granted access to a resource when the node extracts theportion of the token from the waveguide 1102 during of the time slotassociated with the priority level selected by the node.

With reference to FIG. 11, the example timing diagram shown in FIG. 12is described as follows. Because there are only three priority levels, atoken associated with three priority levels is injected into thewaveguide 1102. For the sake of simplicity the duration of the token isapproximately three time slots. In order to inject the token into thewaveguide 1102, the electronic circuit 1120 deactivates the disablingresonator 1118 for a period of three time slots. Because node N0selected priority level 2, beginning at time step 1 node N0 activatesthe resonator 1106 and begins extracting the portion of the tokenassociated with priority level 2 from the waveguide 1102 leaving a gap1214 that subsequently reaches nodes N1, N2, and N3 at time steps 2, 3,and 4, respectively, and reaches detecting resonator D at time step 5.Likewise, nodes N1 and N3 selected priority levels 1 and 3 and extractthe light beginning at time steps 1 and 5 leaving gaps 1215 and 1216,respectively, traveling along the waveguide 1102. The detectingresonator D docs not receive the portion of token associated with thehighest priority level 1 beginning with time step 4. As a result, theelectronic circuit 1120 determines that the highest priority level hasbeen selected by one of the nodes and responds at the beginning of thefirst grant phase 1202 by inactivating the disabling resonator 1118 inorder to inject a token with a duration of one time slot associated withthe highest priority level 1 into the waveguide 1102. In other words, atoken one time slot long is placed on the waveguide 1102 to pass eachnode during the time slot associated with the highest priority level 1.Because node N1 is the only node that selected the highest prioritylevel 1, node N1 activates the resonator 1107 to extract the portion oftoken associated with the highest priority level from the waveguidebeginning at time step 6. Node N1 can then begin using the resource attime step 6. Because portions of the token associated with prioritylevels 2 and 3 are not present light does not pass nodes N0 and N3 attime steps 8 and 10, respectively, which are the time steps marking thetime slots when nodes N0 and N3 can extract light in the grant phase.Thus, nodes N0 and N3 realize they have not been granted access to theresource for the first round of arbitration.

The request phase 2 for the second round of arbitration 1203 begins attime step 10. Table 1206 shows that in the second round of arbitration,nodes N1 and N3 have selected priority levels 3 and 2, respectively, andnodes N0 and N2 have elected not to participate. Nodes N1 and N3 extractthe light beginning at time steps 13 and 14, respectively, leaving gaps1218 and 1219 traveling along the waveguide 1102. The detectingresonator D does not receive light during the time slots beginning withtime steps 15 and 16 and the electronic circuit 1120 responds at thebeginning of the second grant phase 1202 by inactivating the disablingresonator 1118, in FIG. 1, placing a token with a portion associatedwith the highest priority level and the second highest priority levelinto the waveguide 1102. Thus no light reaches node N1 at the beginningof time step 18 when node N1 activates its resonator 1107. As a result,node N1 realizes that it has not been granted access to the resource forthe second round of arbitration. On the other hand, node N3 activatesits resonator 1109 at time step 19 and extracts light during the timeslot associated with priority level 2. As a result, node N3 realizesthat it has been granted access to the resource and can begin using theresource.

The prioritized TDM arbitration method described above with reference toFIG. 12 also favor nodes that lie closest to the optical power source1104. Thus, embodiments of the present invention also allow nodes toincrement or increase the priority level when they have either notachieved a successful request or have not been granted access during thegrant phase. Increasing the priority level can be based on a class ofservice agreement, type of information to be transmitted; global age ofinformation, length of time information has been stored at the node, andpresent length of time before information expires. For example, supposenode N2 is sending VoIP packets that must be sent to avoid interruptionin a communication. In certain embodiments, after each unsuccessfulround of arbitration, node N2 can accordingly increase the prioritylevel. In other embodiments, node N2 can increase the priority levelfollowing an unsuccessful request phase or an unsuccessful grant phase.

C. Summary of Time-Division Multiplexed Arbitration

FIG. 13 shows a control-flow diagram representing steps associated witha method for performing prioritized TDM arbitration for a sharedresource in accordance with embodiments of the present invention. Asshown in FIG. 13, steps 1301-1309 are steps performed during a requestphase, and steps 1309-1318 are steps performed during a grant phase. Instep 1301, a light pulse of a particular wavelength is injected into awaveguide from an optical power source, as described above withreference to FIG. 11. The duration of the light is determined by thenumber of priority levels and the number of time slots used to assert apriority level request. For example, as described above with referenceto FIG. 12, there were only three priority levels and each node assertsa request for the duration of one time slot. Thus, the pulse of lighthas a duration of approximately three time slots. In step 1302, thenodes electing to participate in a round of arbitration and each selectsa priority level for accessing the shared resource. The node electing toparticipate has no knowledge of the priority levels selected by otherparticipating nodes, and thus, each node independently selects apriority level. In the for-loop beginning with step 1303, steps1304-1309 are repeated for each node participating in the request phase.In step 1304, a node activates a resonator to extract a portion of thepulse from the waveguide during the time slot corresponding to thepriority level selected by the node. In step 1305, when the nodeextracts light during the time slot corresponding to the priority levelselected by the node, the method proceeds to step 1306, otherwise, thenode was not successful in extracting the light and the method proceedsto step 1307. In step 1306, the node recognizes that the nodesuccessfully completed the request, deactivates the resonator, and waitsfor the subsequent grant phase to determine whether or not the requestis granted. In step 1307, the node recognizes that the request was notsuccessful, and the node waits for a later round of arbitration toassert another request. In optional step 1308, a node that isunsuccessful in asserting a request during the request phase canincrement the priority level in order to increase the node's chances ofsuccess in a subsequent round of arbitration. For example, a nodesending VOIP packets may increase to the highest priority level for asubsequent round of arbitration or a node can increment the prioritylevel associated with certain packets that are time stamped and have tobe sent before they expire. In step 1309, when another time slot isavailable, steps 1305-1309 are repeated, otherwise, the method proceedsto step 1310 at the beginning of the grant phase. In step 1310, a pulseof light is injected into the waveguide from an optical power source.The pulse is injected so that the node selecting the highest prioritylevel that is closest to the optical power source along the waveguidecan extract the light during the highest priority level selected by thenode. In the for-loop beginning with step 1311, steps 1312-1317 arerepeated for each time slot in the grant phase. In step 1312, each nodecompleting a successful request phase activates the resonator during thetime slot associated with the priority level selected by the node. Instep 1313, when a node extracts light from the waveguide the methodproceeds to step 1314, otherwise the method proceeds to step 1315. Instep 1314, the node realizes that it is granted access to the resource,and in subsequent step 1316, the node begins using the resource, asdescribed above with reference to FIG. 14. In step 1315, the noderealizes that is has not been granted access, and in optional step 1317,the node increases the node's priority level in a subsequent round ofarbitration. In step 1318, when another time slot in the grant phase isavailable, steps 1312-1316 are repeated, otherwise, proceed to step1319, where the TDM arbitration method is repeated for a subsequentround of arbitration.

D. Schematic Circuit Diagrams of Nodes and the Electronic Circuit

FIG. 14 shows a schematic circuit diagram of electronic components of anode 1400 configured in accordance with embodiments of the presentinvention. The node 1400 represents the configuration of electroniccomponents for each node in FIG. 11. The electronic components include a3-bit request register 1402, a shift register 1404 comprising threeregisters labeled 1-3, two OR gates 1406 and 1408, five AND gates1410-1414, and a grant latch 1416. As shown in FIG. 14, the registers1-3 are arranged in a series with the output of register 1 input toregister 2 and the output of register 2 input to register 3. A logicvalue shifts from one register to the next in accordance with either therising or falling edge of the clock signal CLK. The AND gates 1411-1413each receive as input a first logic value from the 3-bit register 1402and a second logic value from registers 1-3, respectively. The outputsfrom registers 1 and 2 also loop back around and are invertered byinverters, such as inverter 1418, prior to being input to AND gate 1410,which also receives as input request signal at the beginning of eachrequest phase. The outputs of AND gates 1411-1413 are input to the ORgate 1408 which sends an electronic signal that activates the noderesonator 1420 and is input to AND gate 1414. The AND gate 1414 alsoincludes an inverter at the input of a grant signal sent to the AND gate1414 at the beginning of the grant phase. When the resonator 1420 trapslight an electronic signal is generated and sent to the grant latch1416. The grant latch 1416 also receives the system clock CLK.

FIG. 14 also includes an example of a request/grant clock signal 1422and a system clock signal 1424. One complete request/grant clock cycleis shown with the request phase beginning on rising edge 1426 and grantphase beginning on falling edge 1428. For the sake of convenience andsimplicity, it is assumed that there are only three priority levels, andthe request and grant phases are each three system clock cycles long.The 3-bit binary strings “100,” “010,” “001” can represent the prioritylevels 1, 2, and 3, respectively, and the binary string “000” canrepresent no request. At the beginning of a request phase, the 3-bitregister 1402 is loaded with the request for a priority level. A requestsignal clears the grant latch 1416, and a request signal correspondingto logic “1” is input to the AND gate 1410. The OR gate 1406 receives alogic “1” input from the AND gate 1410 and logic “0” from register 3 andinputs a logic “1” to register 1. The shift register 1404 cycles throughthe priorities “100,” “010,” and “001” on the rising edge of each clockcycle during the request phase and cycle once again the priorities forthe grant phase. For example, during the clock cycle 1430, the shiftregister 1404 outputs the logic values “1,” “0,” and “0” to the ANDgates 1411-1413, respectively, and during the clock cycle 1431, theshift register outputs the logic values “0,” “1,” and “0” to the ANDgates 1411-1413, respectively. When the contents of the shift register1404 matches the output from the 3-bit register 1402, the AND gate 1412outputs an electronic signal to the OR gate 1408 and the node resonator1420 is activated. During the grant phase, the grant latch 1416 isloaded when the resonator 1420 is active and extracts a portion of thetoken travelling along the waveguide 1102 corresponding to the prioritylevel selected by the node 1400.

FIG. 15 shows a schematic circuit diagram of electronic components ofthe second electronic circuit 1120 configured in accordance withembodiments of the present invention. The electronic circuit 1120includes an inverter 1502, a NOR gate 1504, AND gates 1506-1508, and ashift register 1510. The shift register 1510 is loaded according to theoutputs of the detecting resonator 1114. At the beginning of a requestphase, the NOR gate 1504 receives a request signal corresponding tologic “1.” As a result, the NOR gate 1304 docs not output a signal tothe disable resonator 1118 and the disable resonator 1118 remainsinactive during the request phase so that a token with a three clockcycle duration can be placed on the waveguide 1102. In the requestphase, the results of the arbitration shift to the shift register 1510.When there are multiple priority level requests, the logic gates 1507and 1506 ensure that only the first of multiple request is set, so thatat the end of the request phase the shift register 1510 contains asingle set bit in the position of the highest priority level requestedat register 3 or is empty in the case of no requests. During the grantphase the contents of the shift register 1510 are used to control thedisabling resonator 1118, such that a token is injected into thewaveguide 1102 only for the selected priority level during theappropriate time slot.

III. On-Chip Implementations

The optical arbitration systems 100 and 1100 can be implemented in anoptical layer on a single chip. For example, in certain embodiments, thechip size can be approximately 25×25 mm and have 64 or more nodes. Thewaveguides can have cross-sectional dimensions of approximately 200×500nm, the sets of resonators and detecting resonators, described abovewith reference to FIGS. 1, 9, 10, and 11 can have diameters ranging fromapproximately 20-60 μm, the wavelength selective elements can beseparated by 0.5-5 μm, the diameter of the wavelength selective elementscan range from approximately 1-20 μm. Note that these dimension rangesrepresent exemplary ranges and are by no means intended to limit thebroad range of dimensions over which optical arbitration systems can beemployed. Thus, these dimensions and dimension ranges can vary dependingon the particular implementation.

IV. Microring Resonators

In certain system embodiments, the waveguides can be ridge waveguides,and the wavelength selective elements can be microring resonators. FIG.16A shows an isometric view of a microring resonator 1602 and a portionof an adjacent ridge waveguide 1604 disposed on the surface of asubstrate 1606 and configured in accordance with embodiments of thepresent invention. Light of a particular wavelength transmitted alongthe waveguide 1604 is evanescently coupled from the waveguide 1604 intothe microring 1602 when the wavelength satisfies the resonancecondition:

n_(eff)C=λm

where n_(eff) is the effective refractive index of the microring 1602, Cis the circumference of the microring 1602, m is an integer, and λ isthe wavelength. The product n_(eff)C is the optical length of thecavity. In other words, wavelengths that are integer multiples of thewavelength λ are evanescently coupled from the waveguide 1604 into themicroring 1602.

Evanescent coupling is the process by which evanescent waves of lightare transmitted from one medium, such as microring, to another medium,such a ridge waveguide, and vice versa. For example, evanescent couplingbetween the microring resonator 1602 and the ridge waveguide 1604 occurswhen the evanescent field generated by light propagating in thewaveguide 1604 couples into the microring 1602. Assuming the microring1602 is configured to support the modes of the evanescent field, theevanescent field gives rise to light that propagates in the microring1602, thereby evanescently coupling the light from the waveguide 1604into the microring 1602.

FIG. 16B shows a plot of transmittance versus wavelength for themicroring 1602 and the waveguide 1604 shown in FIG. 16A. Horizontal line1608 represents a wavelength axis, vertical line 1610 represents atransmittance axis, and curve 1612 represent the transmittance of lightpassing the microring 1602 over a range of wavelengths. Thetransmittance of light passing the microring 1602 is defined by:

$T = \frac{I_{out}}{I_{i\; n}}$

where I_(in) is the intensity of the light propagating along thewaveguide 1604 prior to reaching the microring 1602, and I_(out) is theintensity of the light propagating along the waveguide 1604 afterpassing the microring 1602. Minima 1614 and 1616 of the transmittancecurve 1612 correspond to zero transmittance for light having wavelengthsλ_(m)=L/m and λ_(m+1)=L/(m+1), where L is the optical length of thecavity. These wavelengths represent only two of many regularly spacedminima. Wavelengths satisfy the resonance condition above, are said tohave a “strong resonance” with the microring 1602, and are evanescentlycoupled from the waveguide 1604 into the microring 1602. In the narrowwavelength regions surrounding the wavelengths and λ_(m) and λ_(m+1),the transmittance curve 1612 reveals a steep increase in thetransmittance the farther the wavelength is away from the wavelengthsλ_(m) and λ_(m+1). In other words, the strength of the resonancedecreases, and the portion of the light coupled from the waveguide 1604into the microring 1602 decreases the farther the wavelength is awayfrom a resonant wavelength. Light with wavelengths in the regions1618-1620 pass the microring 1602 substantially undisturbed.

Because of the evanescent coupling properties of microring resonators,microring resonators can be operated as detecting resonators, such asdetecting resonators 111-114, to detect particular wavelengthstransmitting along an adjacent waveguide. FIG. 17 shows the microringresonator 1602 coupled to a detecting resonator portion 1702 inaccordance with embodiments of the present invention. Light having awavelength that is resonant with the microring 1602 is evanescentlycoupled from the waveguide 1604 into the microring 1602 and remainstrapped for a period of time while circulating within the waveguide1602. The detecting resonator portion 1702 can be a SiGe doped region ofthe microring 1602. The detecting resonator portion 1702 absorbs thelight circulating in the microring 1602 and converts the light into anelectronic signal that can be transmitted over signal lines to anelectronically coupled node. In other embodiments, the light trappedwithin the microring 1602 can be evanescently coupled in a secondwaveguide and carried to a detector.

The microring 1602 can be electronically tuned by doping regions of thesubstrate 1606 surrounding the microring 1602 and waveguide 1604 withappropriate electron donor and electron acceptor atoms or impurities.FIG. 18 shows a schematic representation and top view of doped regionssurrounding the microring 1602 and the ridge waveguide 1604 inaccordance with embodiments of the present invention. In certainembodiments, the microring 1602 comprises an intrinsic semiconductor. Ap-type semiconductor region 1801 can be formed in the semiconductorsubstrate interior of the microring 1702, and n-type semiconductorregions 1802 and 1803 can be formed in the semiconductor substrate 1606surrounding the outside of the microring 1602 and on the opposite sideof the waveguide 1604. The p-type region 1801 and the n-type regions1802 and 1803 form a p-i-n junction around the microring 1602. In otherembodiments, the dopants can be reversed in order to form an n-typesemiconductor region 1801 in substrate interior of the microring 1602and p-type semiconductor regions 1802 and 1803 in the substratesurrounding the outside of the microring 1602.

The electronically tunable microring 1602 can be configured toevanescently couple or divert light from an adjacent waveguide when anappropriate voltage is applied to the region surrounding the microring.For example, the electronic controlled microring 1602 can be configuredwith a circumference. C and an effective refractive index n_(eff)′ suchthat light with a wavelength λ propagating along the waveguide 1604 doesnot satisfy the resonance condition as follows:

n′_(eff)C≠mλ

where n′_(eff)C is the optical length of the resonator. The passes themicroring 1602 undisturbed and the microring 1602 is said to be“inactive.” On the other hand, the microring 1602 can be formed withsuitable materials so that when an appropriate voltage is applied to themicroring 1602, the effective refractive index n_(eff)′ shifts to therefractive value n_(eff) and the light satisfies the resonancecondition:

n_(eff)C=mλ

The light is now coupled from the waveguide 1604 into the microring 1602and the microring 1602 is said to be “active.” When the voltage issubsequently turn “off,” the effective refractive index of the microring1602 shifts back to n_(eff)′ and the light propagates along thewaveguide 1604 undisturbed.

Note that system embodiments of the present invention are not limited tomicroring resonators and ridge waveguides. In other embodiments, anysuitable resonator that can be configured to couple with a particularwavelength of light propagating along a waveguide can be used.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the invention.However, it will be apparent to one skilled in the art that the specificdetails are not required in order to practice the invention. Theforegoing descriptions of specific embodiments of the present inventionare presented for purposes of illustration and description. They are notintended to be exhaustive of or to limit the invention to the preciseforms disclosed. Obviously, many modifications and variations arepossible in view of the above teachings. The embodiments are shown anddescribed in order to best explain the principles of the invention andits practical applications, to thereby enable others skilled in the artto best utilize the invention and various embodiments with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the followingclaims and their equivalents:

1. An optical arbitration system (100,1100) comprising: a waveguide(102,1102) having a first end and a second end; a source (104,1104)optically coupled to the first end of the waveguide and configured toinput at least one wavelength of light into the waveguide; a number ofwavelength selective elements (106-109,1106-1109) optically coupled tothe waveguide, wherein each wavelength selective element is coupled to anode and is capable of extracting and detecting a wavelength of lightcarried by the waveguide; and an arbiter (110,116,120,1112,1116,1120)optically couple to the second end of the waveguide and opticallycoupled to the waveguide between the source and a wavelength selectiveelement located closest to the source along the waveguide.
 2. The systemof claim 1 wherein the wavelength selective elements include resonators.3. The system of claim 3 wherein the waveguide is a ridge waveguide. 4.The system of claim 1 wherein the arbiter further comprises: a detectionelement (110,1112) disposed near the second end of the waveguide andconfigured to detect at least one wavelength of the light reaching, thesecond end of the waveguide; a filter (116,1116) disposed between thesource and the wavelength selective element located closest to thesource along the waveguide; and an electronic circuit (120,1120)electronically coupled to the detection element and the filter, whereinthe electronic circuit receives electronic signals from the detectionelement and in response to the electronic signals accordingly activatesthe filters to selectively remove at least one wavelength from the atleast one wavelengths output from the source.
 5. The system of claim 4wherein the detection element further comprises at least one detectingwavelength selective element (111-114,1114) optically coupled to thewaveguide near the second end of the waveguide and electronicallycoupled to the electronic circuit, the at least one detecting wavelengthselective element configured to detect at least one of the wavelengthsof light input to the waveguide and send an electronic signal to theelectronic circuit.
 6. The system of claim 4 the filter furthercomprises at least one disabling wavelength selective element(117-119,1118) optically coupled to the waveguide and electronicallycoupled to the electronic circuit between the source and the wavelengthselective element located closest to the source along the waveguide,wherein the at least one disabling wavelength selective element iscapable of extracting at least one of the wavelengths of light whenactivated.
 7. A method for performing prioritized optical arbitration ofa shared resource, the method comprising: injecting multiple wavelengthsof light into a waveguide (601), wherein the waveguide is opticallycouple to each node in a multi-node system and each wavelengthcorresponds to a particular priority level; and requesting access to theresource for a period of time (602-605), each node attempting to extracta wavelength corresponding to a priority level selected by the node fromthe waveguide; and granting one of the nodes access to the resource(608-613), wherein the node granted access successfully extracted fromthe waveguide the wavelength corresponding to the highest selectedpriority level.
 8. The method of claim 7 wherein injecting multiplewavelengths of light into the waveguide further compriseswavelength-division multiplexing the multiple wavelengths into thewaveguide.
 9. The method of claim 7 further comprising determining(604-606) which wavelengths are extracted by the nodes requesting accessto the resource; and filtering out wavelengths (610-612) associated withpriority levels that are lower than the wavelength associated with thehighest selected priority level.
 10. The method of claim 7 whereingranting one of the nodes access to the resource further comprises thenode extracting the wavelength associated with the highest selectedpriority level beyond the period of time for requesting access to theresource.
 11. The method of claim 7 further comprising increasing thepriority level (607,614) for nodes failing to obtain access to theresource based on one or more of: class of service agreement; type ofinformation; global age of information; length of time information hasbeen stored at the node; and present length of time before informationexpires.
 12. A method for performing prioritized optical arbitration ofa shared resource, the method comprising: injecting a pulse of lightinto a waveguide optically couple to each node in a multi-node system(1301); requesting access to the resource for a period of time(1302-1309), wherein each node attempts to extract a portion of thepulse during a time slot associated with a priority level selected bythe node; and granting one of the nodes access to the resource(1310-1318), wherein the node granted access successfully extracted theportion of light in the time slot associated with the highest selectedpriority level.
 13. The method of claim 12 further comprisingdetermining which time slots are extracted by the nodes requestingaccess to the resource (1305-1307); and filtering out time slotsassociated with priority levels having lower priority than the timeslots associated with the highest selected priority level (1310-1318).14. The method of claim 12 wherein granting one of the nodes access tothe resource further comprises the node extracting the light during thetime slot associated with the highest selected priority level after theperiod of time for requesting access to the resource (1312).
 15. Themethod of claim 12 further comprising increasing the priority level(1308,1317) for nodes failing to obtain access to the resource based onone or more of: class of service agreement; type of information; globalage of information; length of time information has been stored at thenode; and present length of time before information expires.